Anodized aluminum alloy material having both durability and low polluting property

ABSTRACT

An anodized aluminum alloy material is formed of an aluminum alloy having a Mg content between 0.1 and 2.0% by mass, a Si content between 0.1 and 2.0% by mass, a Mn content between 0.1 and 2.0% by mass, and an Fe, a Cr and a Cu content of 0.03% by mass or below and containing Al and unavoidable impurities as other components, and is coated with an anodic oxide film. Parts of the anodic oxide film at different positions with respect to thickness of the anodic oxide film have different hardnesses, respectively, and the difference in Vickers hardness between a part having the highest hardness and a part having the lowest hardness is Hv 5 or above.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an aluminum alloy material and, moreparticularly, to an anodized aluminum alloy material intended forforming members of the vacuum chambers of apparatuses for manufacturingsemiconductor devices and liquid crystal devices, such as CVD systems,PVD systems, ion-implanting systems, sputtering systems and dry etchingsystems, and those placed in the vacuum chambers.

2. Description of the Related Art

Reactive gases, etching gases, and corrosive gases containing halogen asa cleaning gas are supplied into the vacuum chambers of apparatuses formanufacturing semiconductor devices and liquid crystal devices, such asCVD systems, PVD systems, ion-implanting systems, sputtering systems anddry etching systems. Therefore, the vacuum chambers are required to havecorrosion resistance to corrosive gases (hereinafter, referred to as“corrosive gas resistance”). Since a halogen plasma is often produced inthe vacuum chamber, resistance to plasmas (hereinafter, referred to as“plasma resistance”) is also important (refer to JP-A Nos. 2003-34894and 2004-225113). Recently, aluminum and aluminum alloy materials havebeen used for forming the members of the vacuum chamber because aluminumand aluminum alloy materials are light and excellent in thermalconductivity.

Since aluminum and aluminum alloy materials are not satisfactory incorrosive gas resistance and plasma resistance, various surface qualityimproving techniques for improving those properties have been proposed.However, those properties are still unsatisfactory and furtherimprovement of those properties is desired.

Coating an aluminum or an aluminum alloy material with a hard anodicoxide film having a high hardness is effective in improving plasmaresistance. The hard anodic oxide film is resistant to the abrasion of amember by a plasma having high physical energy and hence is capable ofimproving plasma resistance (refer to JP-A 2004-225113).

Although the plasma resistance may be improved simply by coating analuminum or an aluminum alloy material with a hard anodic oxide film,the hard anodic oxide film is liable to crack. Once cracks penetrate theanodic oxide film, the corrosive gas reaches the aluminum or thealuminum alloy body of the anodized aluminum or aluminum alloy memberthrough the cracks penetrating the anodic oxide film (hereinafter,referred to as “through cracks”) and the aluminum or the aluminum alloymaterial is corroded.

Therefore, an anodic oxide film having not only a high hardness, butalso durability (crack resistance and corrosive gas resistance) isdesired.

When the Fe content of an aluminum alloy is reduced with a view tosuppress the contamination of a semiconductor wafer or a substrate for aliquid crystal display with Fe, an anodic oxide film having a low Fecontent can be formed. However, such an anodic oxide film is harder, andthe crack resistance and durability of such an anodic oxide film areworse. Therefore, this field desires improving durability (crackresistance and corrosive gas resistance) without enhancing pollutingproperty.

SUMMARY OF THE INVENTION

The present invention has been made in view of the foregoing problemsand it is therefore an object of the present invention to provide ananodized aluminum alloy having a high hardness, durability and lowpolluting property.

An anodized aluminum alloy material in a first aspect of the presentinvention is formed of an aluminum alloy having a Mg content between 0.1and 2.0% (“%” signifies “mass %” herein unless otherwise specified), aSi content between 0.1 and 2.0%, a Mn content between 0.1 and 2.0%, andan Fe, a Cr and a Cu content of 0.03% or below and containing Al andunavoidable impurities as other components, and is coated with an anodicoxide film; wherein parts of the anodic oxide film at differentpositions with respect to the thickness of the anodic oxide film havedifferent hardnesses, respectively, and the difference in Vickershardness between a part having the highest hardness and a part havingthe lowest hardness is Hv 5 or above.

The anodized aluminum alloy material has a high hardness, durability andlow polluting property.

In the anodized aluminum alloy material in the first aspect of thepresent invention, the hardness of the part having the lowest hardnessof the anodic oxide film is Hv 365 or above, which leads to improvementof plasma resistance.

The aluminum alloy forming the anodized aluminum alloy material has a Mgcontent between 0.1 and 2.0%, a Si content between 0.1 and 2.0%, a Mncontent between 0.1 and 2.0%, and an Fe, a Cr and a Cu content of 0.03%or below and contains Al and unavoidable impurities as other components,the anodized aluminum alloy material is coated with the anodic oxidefilm, parts of the anodic oxide film at different positions with respectto the thickness of the anodic oxide film have different hardnesses,respectively, and the difference in Vickers hardness between a parthaving the highest hardness and the part having the lowest hardness ofthe anodic oxide film is Hv 5 or above. Therefore, the anodized aluminumalloy material has a high hardness, durability and low pollutingproperty.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described in terms of preferredembodiments thereof.

Composition of Aluminum Alloy Forming Anodized Aluminum Alloy Material

An anodized aluminum alloy material according to the present inventionis formed of an aluminum alloy having a Mg content between 0.1 and 2.0%,a Si content between 0.1 and 2.0%, a Mn content between 0.1 and 2.0%,and an Fe, a Cr and a Cu content of 0.03% or below and containing Al andunavoidable impurities as other components, and is coated with an anodicoxide film. Parts of the anodic oxide film at different positions withrespect to the thickness of the anodic oxide film have differenthardnesses, respectively, and the difference in Vickers hardness betweena part having the highest hardness and a part having the lowest hardnessis Hv 5 or above. Thus the anodized aluminum alloy material has a highhardness, durability and low polluting property.

Reasons for determining the foregoing composition will be described.

The inventors of the present invention placed restrictions on the Fe,the Cr and the Cu content of the aluminum alloy so that a workpiece of asemiconductor or the like may not be contaminated. Effect of limitingthe Fe content at a low level on increasing the hardness of the anodicoxide film and ensuring plasma resistance was utilized positively andstudies were made to find out measures for preventing the growth ofcracks formed in the anodic oxide film to the aluminum alloy body of theanodized aluminum alloy material. It was found through the studies thatthe growth of cracks formed in the anodic oxide film to the aluminumalloy body of the anodized aluminum alloy material can be prevented byproperly determining process conditions for forming the anodic oxidefilm such that parts of the anodic oxide film at different positionswith respect to the thickness of the anodic oxide film have differenthardnesses, respectively, and the difference in Vickers hardness betweena part having the highest hardness and a part having the lowest hardnessis Hv 5 or above. Thus the penetration of a gas through the anodic oxidefilm to the aluminum alloy material was suppressed and generaldurability was ensured. Details of a mechanism of the compositioncapable of solving the foregoing problems have not been elucidated.However, it is inferred that stress causing a crack to grow is absorbedby a part having a low hardness of the anodic oxide film and,consequently, the crack cannot grow to the aluminum alloy body of theanodized aluminum alloy material.

The present invention will be described in detail.

Components of Aluminum Alloy

Although details of a mechanism is not clearly known, it is inferredthat an anodic oxide film is strengthened when a Mg₂Si compound, and anAl—Mn—Si compound or an Al—Mn compound are combined with Mg, Si and Mncontained in an aluminum alloy.

Mg Content: 0.1 to 2.0%

Magnesium (Mg) is an element necessary for producing a Mg₂Si compound. AMg₂Si compound is produced scarcely and a desired effect on improvingthe durability of the anodic oxide film cannot be achieved when the Mgcontent is below 0.1%. Coarse grains of a Mg₂Si compound are formed toobstruct formation of a normal anodic oxide film when the Mg content isabove 2.0%. Therefore, a proper Mg content is between 0.1 and 2.0%,preferably, 0.8%.

Si Content: 0.1 to 2.0%

Silicon (Si), as well as Mg, is an element necessary for producing aMg2Si compound. A Mg₂Si compound is produced scarcely and a desiredeffect on improving the durability of the anodic oxide film cannot beachieved when the Si content is below 0.1%. Coarse grains of a Mg₂Sicompound are formed to obstruct formation of a normal anodic oxide filmwhen the Si content is above 2.0%. Therefore, a proper Si content isbetween 0.1 and 2.0%, preferably, 1.2%.

Mn Content: 0.1 to 2.0%

Manganese (Mn) is an element necessary for producing an Al—Mn—Sicompound or an Al—Mn compound. An Al—Mn—Si compound or an Al—Mn compoundis produced scarcely and a desired effect on improving the durability ofthe anodic oxide film cannot be achieved when the Mn content is below0.1%. Coarse grains of the compound are formed to obstruct formation ofa normal anodic oxide film when the Mn content is above 2.0%. Therefore,a proper Mn content is between 0.1 and 2.0%, preferably, 1.6%.

Fe, Cr and Cu Contents: 0.03% or Below Each

Electricity for an anodizing process is used for ionizing Al and forgenerating oxygen through the electrolysis of water. If the ratio of anamount of electricity for producing oxygen is high, the ratio of anamount of electricity for the ionization of Al decreases is low,aluminum oxide cannot be efficiently produced and film formation ratedecreases. When the aluminum alloy contains Fe, Cr and Cu, generation ofoxygen starts from those elements and the ratio of the amount ofelectricity for oxygen generation increases and, consequently, the filmforming rate decreases. If each of the Fe, the Cr and the Cu content isabove 0.03%, Fe, Cr and Cu are emitted from the aluminum alloy body andthe anodic oxide film into a gas and a workpiece of a semiconductor orthe like is contaminated. Therefore, each of the Fe, the Cr and the Cucontent is 0.03% or below, preferably, 0.01% or below.

Al and Unavoidable Impurities as Other Elements

Substantially, Al is only the other element. However, the aluminum alloycontains, in addition to Fe, Cr and Cu, unavoidable impurities includingNi, Zn, B, Ca, Na and K in unavoidably low contents. Preferably, thetotal of the unavoidable impurity contents other than the Fe, the Cr andthe Cu content is 0.1% or below.

A crystalline pattern is formed in the anodic oxide film and anodicoxide film has an irregular color tone if the aluminum alloy grains arecoarse. Titanium (Ti) may be added to the aluminum alloy to prevent thegrowth of coarse aluminum alloy grains. An excessively low Ti contentdoes not have a grain size control effect. An excessively high Ticontent causes pollution. When Ti is added to the aluminum alloy, alower limit Ti content is 0.01%, preferably, 0. 015%, and an upper limitTi content is 0.03%, preferably, 0.025%.

Method of Manufacturing Aluminum Alloy Material

A method of manufacturing an aluminum alloy material will be described.

An aluminum alloy ingot having the foregoing composition is made by anordinary casting process, such as a continuous casting process, asemi-continuous casting process (DC casting process) or the like. Then,the aluminum alloy ingot is subjected to a homogenizing heat treatment,namely, a soaking process. An anodic oxide film excellent in durabilityis formed by processing the aluminum alloy ingot by the soaking processat a temperature, namely, homogenizing temperature or soakingtemperature, of 500° C. or above. An anodic oxide film having still moreexcellent in durability can be formed by processing the aluminum alloyingot by the homogenizing treatment at a homogenizing temperature above550° C. Burning occurs to deteriorate the surface quality of thealuminum alloy ingot when the homogenizing temperature is above 600° C.Therefore, it is recommended that the homogenizing temperature is in therange of 500° C. (preferably, a temperature not lower than 550° C.) to600° C. although the effect of the homogenizing temperature on theformation of the anodic oxide film is not yet ascertained, it isinferred that the homogenizing temperature participates in producing anAl—Mn—Si compound or an Al—Mn compound as mentioned above.

The aluminum alloy ingot processed by the homogenizing heat treatment isprocessed by a proper plastic working process, such as a rollingprocess, a forging process or an extrusion process, to obtain analuminum alloy material. Then, the aluminum alloy material is subjectedto a solution process, a quenching process and an artificial agingprocess (hereinafter, referred to also simply as “aging process”). Then,the aluminum alloy material is formed in a suitable shape by machiningto obtain an aluminum alloy material. An aluminum alloy slab obtained byprocessing the aluminum alloy ingot may be subjected to the solutionprocess, the quenching process and the aging process to obtain analuminum alloy material. The solution process, the quenching process andthe aging process may be, for example, a solution process at atemperature between 515° C. and 550° C., a water quenching process andan aging process at 170° C. for 8 h or at 155° C. to 165° C. for 18 hforming an ordinary T6 process.

Anodic Oxide Film

An anodic oxide film coating the aluminum alloy material will bedescribed. An anodic oxide film forming method is executed by properlydetermining conditions for electrolysis including the composition andconcentration of an electrolyte, voltage, current density, waveforms ofcurrent and voltage, and temperature for electrolysis. Electrolysis foranodization needs to use an anodizing solution containing at least oneof elements including C, S, N, P and B. For example, it is effective touse an aqueous solution containing at least one of oxalic acid, formicacid, sulfamic acid, phosphoric acid, phosphorous acid, boric acid,nitric acid or its compound, and phthalic acid or its compound. There isnot any particular limit to the thickness of the anodic oxide film. Thethickness of the anodic oxide film is between about 0.1 and about 200μm, preferably, between 0.5 and 70 μm, more desirably, between about 1and about 50 μm.

As mentioned above, parts of the anodic oxide film at differentpositions with respect to the thickness of the anodic oxide film havedifferent hardnesses, respectively, and the difference in Vickershardness between a part having the highest hardness and a part havingthe lowest hardness is Hv 5 or above. Therefore, the anodic oxide filmhas a high hardness, and is capable of suppressing the growth of cracksand excellent in crack resistance. Since the anodic oxide film isexcellent in crack resistance, penetration of gases through the anodicoxide film to the aluminum alloy body is suppressed and generaldurability is ensured. If the difference in Vickers hardness between apart having the highest hardness and a part having the lowest hardnessis below Hv 5, the behavior of the anodic oxide film is equal to that ofan anodic oxide film having a substantially uniform thickness withrespect to a direction parallel to the width, it is difficult for theanodic oxide film to suppress the growth of cracks. Consequently, theanodic oxide film has low crack resistance and low corrosive gasresistance.

According to the present invention, the anodic oxide film should have atleast two parts at different positions with respect to the thickness ofthe anodic oxide film having different hardnesses. The number of suchparts is not limited to any number, provided that the number is two orgreater. The hardness of the anodic oxide film may discontinuouslychange or may continuously change in a slope.

From the viewpoint of suppressing the growth of cracks created in theanodic oxide film, it is considered that the part having the lowesthardness has the lowest possible Vickers hardness. However it isdesirable, from the viewpoint of ensuring resistance to the abrasiveeffect of the physical energy of plasma, that the part has a hardness ofHv 365 or above.

An aluminum alloy material coated with the anodic oxide film(hereinafter, referred to as “anodized aluminum alloy material”) issuitable for forming members to be used in a high-temperature corrosiveatmosphere. The anodized aluminum alloy material is particularlysuitable for forming a vacuum chamber for a plasma processing apparatusincluded in a semiconductor device manufacturing system or the like, andparts placed in the vacuum chamber, such as electrodes, which areexposed to a corrosive gas in a high-temperature atmosphere and arerequired to have a low contaminating property of contaminatingworkpieces.

An anodic oxide film having parts at different positions with respect tothe thickness of the anodic oxide film respectively having differenthardnesses can be formed by a method that changes the temperature of ananodizing solution intermittently or continuously during an anodizingprocess, or a method that interrupts an anodizing process using ananodizing solution, takes out the aluminum alloy material from theanodizing solution, and resumes an anodizing process using an anodizingsolution of a different composition and/or a different temperature.Those methods can form an anodic oxide film having parts at differentpositions with respect to the thickness respectively having differenthardnesses. An anodizing solution of a lower temperature is moreeffective in suppressing the chemical dissolution of an anodic oxidefilm during the anodizing process and in forming a hard anodic oxidefilm.

As mentioned above, when the Fe content of an aluminum alloy is reducedto 0.03% or below with a view to suppress the contamination of aworkpiece, such as a semiconductor wafer, the Fe content of an anodicoxide film can be reduce to 500 ppm or below. The Fe content of ananodic oxide film can be reduce to 150 ppm or below when the Fe contentof the aluminum alloy is reduced to 0.01% or below.

As mentioned above the anodized aluminum alloy material has a highhardness and is satisfactory in durability (crack resistance andcorrosive gas resistance) and low contaminating property.

EXAMPLES

Examples of the present invention will be described. Examples describedherein do not place any limit to the present invention and changes thatmay be made therein without departing from foregoing and the followinggist are within the technical scope of the present invention.

Aluminum alloy ingots of 220 mm in width, 250 mm in length and 100 mm inthickness having the compositions of examples of the present invention,namely, Samples Nos. 1, 2,4 and 5, and comparative examples, namely,samples Nos. 3 and 6 to 14 shown in Table 1 were formed by casting andwere cooled at a cooling rate in the range of 10 to 15 ° C./s. Thealuminum alloy ingots were cut and ground to obtain aluminum alloy slabsof 220 mm in width, 150 mm in length and 60 mm in thickness. Thealuminum alloy slabs were processed by a soaking process at 540° C. for4 h. The soaked aluminum alloy slabs of 60 mm in thickness weresubjected to a hot rolling process to obtain aluminum alloy plates of 6mm in thickness. Sample alloy plates were obtained by processing thealuminum alloy plates by a solution treatment at a temperature in therange of 510° C. to 520° C. for 30 min, a water quenching process, andan aging process at a temperature in the range of 160° C. to 180° C. for8h. Specimens of 25 mm×35 mm (rolling direction) and 3 mm in thicknesswere cut out from the alloy plates. The surfaces of the specimens wereground in a surface roughness of Ra 1.6.

TABLE 1 Durability Polluting property Content Corroded Fe Cr Cu (% bymass) Hardness area ratio content content content Specimen No. Mg Si MnFe Cr Cu difference (%) Judgment (ppm) (ppm) (ppm) Judgment 1 Ex. 0.81.2 1.6 0.008 0.009 0.007 10 0 ⊚ 150 190 130 ⊚ 2 Ex. 0.8 1.2 1.6 0.0080.009 0.007 5 2 ◯ 150 190 130 ⊚ 3 Comp. 0.8 1.2 1.6 0.008 0.009 0.007 410 X 160 180 150 ⊚ ex. 4 Ex. 0.1 0.1 0.1 0.029 0.028 0.027 10 3 ◯ 490480 480 ◯ 5 Ex. 1.9 2.0 1.8 0.027 0.028 0.028 10 3 ◯ 470 480 490 ◯ 6Comp. 0.09 0.8 1.1 0.006 0.008 0.009 10 11 X 120 170 190 ⊚ ex. 7 Comp.2.1 0.8 1.0 0.007 0.009 0.008 10 18 X 130 180 170 ⊚ ex. 8 Comp. 1.0 0.080.7 0.009 0.007 0.008 10 9 X 170 150 160 ⊚ ex. 9 Comp. 1.0 2.1 0.8 0.0080.006 0.009 10 20 X 160 130 180 ⊚ ex. 10  Comp. 0.9 1.1 0.09 0.008 0.0090.006 10 10 X 150 180 130 ⊚ ex. 11  Comp. 1.1 0.9 2.1 0.009 0.008 0.00710 19 X 180 160 140 ⊚ ex. 12  Comp. 0.9 1.0 0.9 0.031 0.007 0.008 10 0 ⊚520 140 180 X ex. 13  Comp. 1.0 1.0 0.9 0.008 0.032 0.009 10 0 ⊚ 170 530190 X ex. 14  Comp. 1.0 0.9 0.9 0.007 0.009 0.031 10 0 ⊚ 140 190 510 Xex. Second anodic oxide film First anodic oxide film Tempera- Thick-Hard- Temperature Voltage Thickness Hardness ture Voltage ness nessSpecimen No. Anodizing solution (° C.) (V) (μm) (Hv) Anodizing solution(° C.) (V) (μm) (Hv) 1 Oxalic acid solution 10 60 15 380 Oxalic acidsolution 5 60 15 390 (Concentration: 25 g/l) (Concentration: 25 g/l) 2Oxalic acid solution 8 60 15 385 Oxalic acid solution 5 60 15 390(Concentration: 25 g/l) (Concentration: 25 g/l) 3 Oxalic acid solution 760 15 386 Oxalic acid solution 5 60 15 390 (Concentration: 25 g/l)(Concentration: 25 g/l) 4 Oxalic acid solution 10 60 15 365 Oxalic acidsolution 5 60 15 375 (Concentration: 25 g/l) (Concentration: 25 g/l) 5Oxalic acid solution 10 60 15 365 Oxalic acid solution 5 60 15 375(Concentration: 25 g/l) (Concentration: 25 g/l) 6 Oxalic acid solution10 60 15 380 Oxalic acid solution 5 60 15 390 (Concentration: 25 g/l)(Concentration: 25 g/l) 7 Oxalic acid solution 10 60 15 380 Oxalic acidsolution 5 60 15 390 (Concentration: 25 g/l) (Concentration: 25 g/l) 8Oxalic acid solution 10 60 15 380 Oxalic acid solution 5 60 15 390(Concentration: 25 g/l) (Concentration: 25 g/l) 9 Oxalic acid solution10 60 15 380 Oxalic acid solution 5 60 15 390 (Concentration: 25 g/l)(Concentration: 25 g/l) 10  Oxalic acid solution 10 60 15 380 Oxalicacid solution 5 60 15 390 (Concentration: 25 g/l) (Concentration: 25g/l) 11  Oxalic acid solution 10 60 15 380 Oxalic acid solution 5 60 15390 (Concentration: 25 g/l) (Concentration: 25 g/l) 12  Oxalic acidsolution 10 60 15 360 Oxalic acid solution 5 60 15 370 (Concentration:25 g/l) (Concentration: 25 g/l) 13  Oxalic acid solution 10 60 15 380Oxalic acid solution 5 60 15 390 (Concentration: 25 g/l) (Concentration:25 g/l) 14  Oxalic acid solution 10 60 15 380 Oxalic acid solution 5 6015 390 (Concentration: 25 g/l) (Concentration: 25 g/l) (Note) Examplesare abbreviated to Exs. and Comparative examples to Comp. exs.

Each of the specimens was immersed in a 10% NaOH solution of 60° C. for2 min, the specimen was rinsed with water, the specimen was immersed ina 20% HNO₃ solution of 20° C. for 2 min, and then the specimen wasrinsed with water to clean the surface thereof. Then, a first anodicoxide film was formed on a surface of the specimen and a second anodicoxide film was formed on the first anodic oxide film by an anodizingprocess. Process conditions for the anodizing process are shown inTable 1. The first and the second anodic oxide film were formed in athickness of 15 μm using a processing solution having an oxalicconcentration of 25 g/L (the letter “L” represents “liter”). Bathvoltage was fixed at 60 V. The difference between the anodizingconditions respectively for the forming the first and the second anodicoxide film was only the temperature of the processing solution. Thetemperature of the processing solution for forming the first anodicoxide film was higher than that for forming the second anodic oxidefilm.

The Fe, the Cr and the Cu content of the anodized aluminum alloyspecimens (hereinafter referred to simply as “specimens”) were measured,the hardness of the anodic oxide films was measured, and the durabilityof the anodic oxide films was tested.

Measurement of Fe, Cr and Cu Contents of Anodic Oxide Film

Contaminating properties of the specimens were evaluated. The specimenwas immersed in 100 ml of a 7% hydrochloric acid solution to dissolvethe anodic oxide film to the extent that the aluminum alloy body is notexposed. The weight W (g) of the dissolved anodic oxide film wasdetermined by calculating the difference in weight between the weight ofthe hydrochloric acid solution before the dissolution of the anodicoxide film and that of the same after the dissolution of the anodicoxide film. Then, the Fe, the Cr and the Cu content of the hydrochloricacid solution were determined through the ICP analysis of thehydrochloric acid solution, and the respective weights W_(Fe), W_(Cr)and W_(Cu) (g) of Fe, Cr and Cu contained in 100 ml of the hydrochloricacid were calculated. Then, the Fe, the Cr and the Cu content of theanodic oxide film, namely, W_(Fe)/W W_(Cr)/W and W_(Cu)/W, werecalculated. The contaminating property of the specimen was evaluated bythe Fe, the Cr and the Cu content of the anodic oxide film on the basisof the following criterion. Results of evaluation are shown in Table 1.

Criterion for Contaminating Property Evaluation

Double circle: All the Fe, the Cr and the Cu content are 300 ppm orbelow

Circle: At least one of the Fe, the Cr and the Cu content is above 300ppm and 500 ppm or below and other elements are 300 ppm or below

Cross: At least one of the Fe, the Cr and the Cu content is above 500ppm

Results of Evaluation of Polluting Property

As shown in Table 1, some of the Fe, the Cr and the Cu content of theanodic oxide films of the specimens Nos. 12 to 14 of the comparativeexamples was above 500 ppm. All of the Fe, the Cr and the Cu content ofthe specimens Nos. 1, 2, 4 and 5 of the examples and the specimens Nos.3 and 6 to 11 of the comparative examples were satisfactorily as low as500 ppm or below. As shown in Table 1, all of the Fe, the Cr and the Cucontent of the specimens Nos. 1 and 2 of the examples and the specimensNos. 3 and 6 to 11 of the comparative examples were very low values of300 ppm or below and those examples and comparative examples were verysatisfactory.

Measurement of Hardness of Anodic Oxide Film

Each specimen was embedded in a resin, a cross section of the specimenincluding sections of the anodic oxide film and the aluminum alloy bodywas polished. The hardness of the polished section of the anodic oxidefilm was measured by a measuring method specified in Z2244 (1998), JIS.

Results of Measurement

In each of the specimens Nos. 1, 2, 4 and 5 of the examples and thespecimens Nos. 3 and 6 to 14 of the comparative examples, the secondanodic oxide film has a hardness higher than that of the first anodicoxide film. Such a hardness difference between the first and the secondanodic oxide film was caused by a condition that the temperature of theanodizing solution used for forming the second anodic oxide film waslower than that of the anodizing solution used for forming the firstanodic oxide film. The difference in hardness between the first and thesecond anodic oxide film of the specimen No. 2 of the example was Hv 5.Such a hardness difference was caused by a condition that thetemperature of the anodizing solution used for forming the second anodicoxide film was 5° C. and that of the anodizing solution used for formingthe first anodic oxide film was 8° C. The difference in hardness betweenthe first and the second anodic oxide film of the specimen No. 3 of thecomparative example was Hv 4. Such a hardness difference was caused by acondition that the temperature of the anodizing solution used forforming the second anodic oxide film was 5° C. and that of the anodizingsolution used for forming the first anodic oxide film was 7° C. Thedifference in hardness between the first and the second anodic oxidefilm of each of the specimens Nos. 1, 4 and 5 of the other examples andthe SPECIMENS Nos. 6 to 14 of the other comparative examples was Hv 10.Such a hardness difference was caused by a condition that thetemperature of the anodizing solution used for forming the second anodicoxide film was 5° C. and that of the anodizing solution used for formingthe first anodic oxide film was 10° C. Thus the anodic oxide film can beformed in an optional hardness by controlling the temperature of theanodizing solution. As shown in Table 1, the respective hardnesses ofthe anodic oxide films excluding the anodic oxide film of the specimenNo. 12 of the comparative example were Hv 365 or above. Therefore, theplasma resistance of the anodic oxide films excluding the anodic oxidefilm of the specimen no. 12 of the comparative example is satisfactory.

Test of Durability of Anodic Oxide Film

A durability test included a crack resistance test at a first stage anda corrosive gas resistance test at a second stage. In the crackresistance test, a specimen was heated at 450° C. for 1 h in a testvessel of an atmospheric atmosphere, and then the specimen taken outfrom the test vessel was dipped in water of 27° C. for quenching. Thespecimen tested by the crack resistance test was subjected to twocorrosive gas resistance test cycles. Each corrosive gas resistance testcycle held the specimen in a 5% Cl₂—Ar gas atmosphere of 400° C. for 4h. Then, the corroded area ratio of the surface of the specimen wascalculated by using and expression: (Corroded area ratio) {(Area orcorroded parts)/(Area of the surface of the specimen)}×100. Thespecimens were evaluated on the basis of the following criterion.Results of evaluation are shown in Table 1.

Criterion for Durability Evaluation

Double circle: Corroded area ratio 0%

Circle: Corroded area ratio: 0 to 3%

Cross: Corroded area ratio: Above 3%

Results of Durability Evaluation

As shown in Table 1, the specimens Nos. 3 and 6 to 11 of the comparativeexamples were unacceptable. The specimens Nos. 1, 2, 4 and 5 of theexamples and the specimens Nos. 12 to 14 of the comparative exampleswere satisfactory in durability. As shown in Table 1, the specimen No. 1of the example and the specimen Nos. 12 to 14 of the comparativeexamples were very satisfactory in durability.

It is known from the synthetic conclusion based on the measured data onthe Fe, the Cr and the Cu content of the anodic oxide films, themeasured data on the hardness of the anodic oxide films, and the resultsof the durability tests of the anodic oxide films that only thespecimens Nos. 1, 2, 4 and 5 of the examples meet all the criterions.The specimens Nos. 1, 2, 4 and 5 of the examples meeting all thecriterions are have a high hardness and are satisfactory in bothdurability and low polluting property.

1. An anodized aluminum alloy material formed of an aluminum alloyhaving a Mg content between 0.1 and 2.0% by mass, a Si content between0.1 and 2.0% by mass, a Mn content between 0.1 and 2.0% by mass, and anFe, a Cr and a Cu content of 0.03% by mass or below and containing Aland unavoidable impurities as other components, and coated with ananodic oxide film; wherein parts of the anodic oxide film at differentpositions with respect to thickness of the anodic oxide film havedifferent hardnesses, respectively, and difference in Vickers hardnessbetween a part having the highest hardness and a part having the lowesthardness is Hv 5 or above.
 2. The anodized aluminum alloy materialaccording to claim 1, wherein the hardness of the part having the lowesthardness of the anodic oxide film is Hv 365 or above.